Numerous elevating devices comprising fluid jacks for controlling elevation are provided with safety valves whose principal function is double: not controlled, these safety valves prevent any accidental return of fluid towards the reservoir; controlled, they allow passage of fluid in the two possible directions of flow.
Certain of these safety valves have an electric control of the position allowing passage of the fluid by opening of the valve. Failures may occur on this electric control, and/or on the mechanical parts coupled thereto, and it has already been provided to overcome such failures, at least temporarily, by means of a voluntary valve-opening control actuated if desired by a user.
According to a known embodiment, a nut maintains the solenoid coil of the electromagnet controlling passage of fluid, in position assembled on the body of the valve, and comprises a bottom, traversed by a screw disposed opposite the core of said electromagnet. In the event of a possible failure, during which the electromagnet no longer controls opening of the valve, it suffices to rotate said screw until it pushes the valve in its position of opening.
However, it has been observed that this emergency valve-opening control itself broke down, this being principally due to the fact that, between the thread of the screw and the corresponding tapping of the bottom of the nut, a permanent clearance existed and allowed the introduction of humidity inside the mechanism, which caused this mechanism to rust, deteriorating both the emergency control and the electromagnetic valve-opening control.
It is an object of the invention to overcome this state of affairs by insulating the internal mechanism from the outside humidity, permanently except possibly temporarily when the voluntary emergency valve-opening control is actuated.